The Truth-teller is the self-referential bit of that sentence: “This sentence is true.”
The Truth-teller is saying only that what it is saying is true (which all sentences implicitly assert anyway), so it is not saying much, and so there is not much for it to be true or false about. It would be consistent for it to be true, and consistent for it to be false, but what could determine which it is? Maybe there is no fact of the matter, what it is. So, is that sentence neither true nor false? But then “This sentence is true” would clearly be false (and the fact that it would refutes the idea that it says nothing at all). Still, it is not saying much, and so it is not very true and not very false. It is therefore fairly false that it is true, and so what little it is saying – that it is true – is fairly false.
The Truth-teller is not saying much, but what it says is more false than true. It may therefore be the case that the Truth-teller is not very true and only about as false as not. To see why that might be possible, consider a man going bald: As he goes bald he will not, by the loss of just one or two hairs, become bald and so there might be an intermediate or overlap stage at which he is about as bald as not, when it would make sense for it to be about as true as not that he was bald, and about as false as not. There is a lot to be said for, and against, such a possibility; here it would be most apposite to look at the Truth-teller’s paradoxical companions.
The following sentence occurs in the preface of a work of fiction: “None of the sentences in this book are true.” If that sentence, say Sent, was true, then none of the sentences in that book would be true, and so Sent in particular would not be true; and that contradiction means, by reductio ad absurdum, that it is not the case that Sent is true. So either Sent is false – in which case at least one of the other sentences would have to be true – or else it is neither true nor false; and it could of course be the case that none of the other sentences are true, so Sent is neither true nor false. But that cannot be because Sent is meaningless, because we have just been reasoning logically with its meaning.
Sent does have two obvious meanings, though. As well as the one we have been working with (its literal meaning), it was clearly supposed to be saying that none of the other sentences in that book were true. And since it did express that latter meaning (which we might call its literary meaning) clearly enough for us to notice, hence it did also have that meaning. So, if none of the other sentences were true, then it would be true that none of them were true, and so in a sense Sent would be true (with the literary meaning) and not false; and it would false that there was not even that truth, and so in a sense Sent would not be true (applying the literal meaning) but would be false. It follows that Sent is false: If it is not false because one of the other sentences is true, then it is still false because it is in another sense true.
Working with only the literal meaning was paradoxical, though; it left us with something like a reductio of the logical presumption that sentences are either true or else not true. Logic, and language itself, suit veracity and falsity being black and white, but there is also vagueness; and we do want to think something veridical about paradoxical sentences. So, the actual reductio above should be replaced by: Insofar as Sent is true, Sent is not true. It follows that Sent, taken literally, is about as true as not. Still, it is more realistic to read it as being true if none of the other sentences are. So for simplicity, let us consider the paradoxical bit by itself: “This sentence is not true.”
That sentence (the Liar) is saying that what it is saying is not true. Unlike the Truth-teller, it is not just saying something that all sentences implicitly assert, so it does not seem to be saying nothing; and note that if it was saying nothing, then it would not be saying anything true, whence it would clearly be true. So, Liar is paradoxical; insofar as Liar is true, it is not true, and insofar as it is false it is true. It follows that Liar is about as true as not, and about as false as not: It is to some extent true, that it is not true, because it is only to some extent true; and it is not exactly false that it is not true, because it is to some extent false.
For a final complication: “This sentence is not true, and not even about as true as not.” If that sentence, say Even, is about as true as not, then Even is saying something false. Nevertheless, Even, by saying that Even is far from true, is thereby saying that it is far from true that Even is far from true. So although Even is saying something that is false, it is something that is also true, and about as true as not. Consequently Even can be about as true as not, and about as false as not.